Such arrangements are used in wattmeters for example, or in electricity counters to form a voltage/current product u.sub.N.i.sub.N or, while the voltaqe u.sub.N is kept constant, to measure an electric current i.sub.N. In this case u.sub.N preferably designates the supply voltage of an electrical power network and i.sub.N the electric current consumed by a user of electric energy. Since the current i.sub.N is proportional to a magnetic field induction B.sub.N which it produces, the magnetic field sensor measures the current i.sub.N indirectly when it measures the magnetic field induction B.sub.N. Since the output voltage u.sub.H of a Hall element used as a magnetic field sensor is proportional to the product i.B.sub.N, where i is the supply current of the Hall element, the Hall element also provides the voltage/current product u.sub.N. i.sub.N when the supply current i of the Hall element is produced in proportion to the network voltage u.sub.N by means of a voltage/current converter.
When magnetic field sensors are used in precision instruments, the requirements for their longterm stability are correspondingly high, and such longterm stability cannot be taken for granted when incorporation in an integrated circuit is involved. Among other factors, small changes in the charge-carrier concentration of the semiconductor material affects the longterm stability of a magnetic field sensor made of a semiconductor material.
The changes in charge-carrier concentration of the semiconductor material of a magnetic field sensor, e.g. due to "traps" in the energy bandgap, influence the output voltage of the magnetic field sensor directly and thereby its longterm stability. Any introduction of impurities in one of the manufacturing processes can produce charge-carriers in the sensitive area of the magnetic field sensor through subsequent diffusion of ions into that area and can lead to a change of the magnetic field sensor's sensitivity. No solution has been provided up to now concerning the reduction of the negative influence of the above-mentioned effects on the long-term stability.
In view of the above, it is an object of the present invention to provide an arrangement which eliminates or at least greatly reduces the negative influence of small variations in the charge-carrier concentration of the semiconductor material upon the longterm stability of a magnetic field sensor.